class Son{
       public static void main (String args []) {
		   Scanner score = new Scanner(System.in);
		   if ( 100 >= score > 80){
               System.out.println ("A");}
		   else if ( 80 >= score > 70){
               System.out.println ("B");} 
		   else if ( 70 >= score > 60){
			   System.out.println ("c");}
		   else if ( 60 >= score >= 0){
			   System.out.println ("D");}
	   }
}